1. Field of the Invention
The present invention relates in general to an engine, and more particularly to control sensors of a marine engine used to precisely control the fuel/air mixture delivered to combustion chambers of the engine.
2. Description of Related Art
Several outboard motors recently have become equipped with engine control systems in response to increased concerns of hydrocarbon emissions. Such systems closely monitor and control the fuel/air ratio of the fuel charge delivered to each cylinder of the engine. The engine control system can significantly reduce hydrocarbon emissions, while improving fuel economy and engine performance.
An engine control system often includes a throttle sensor which detects the opening degree of a throttle device associated with the engine. For instance, such prior throttle sensor detects the angular position of the throttle valves and sends a signal indicative of the throttle valve position to an electronic control unit of the engine control system. The electronic control unit uses this information to determine the intake airflow rate into the cylinders of the engine and to adjust the amount of fuel delivered to the engine cylinders to obtain a desired fuel/air ratio.
Prior throttle sensors often are directly attached to the intake manifold or throttle body and are coupled to the throttle shaft. A thin band commonly connects a shaft of the throttle sensor to the throttle shaft. The use of this type of coupling, however, in the conventional mounting arrangement produces several disadvantages.
As a result of the direct coupling provided by the thin band, the thin band absorbs engine vibrations which it transmits to the throttle sensor. Such vibrations negatively effect the performance of the throttle sensor. In addition, the thin band commonly twists slightly when the throttle shaft rotates. The shaft of the throttle sensor thus follows the throttle shaft with a slight delay. As a result, hysteresis occurs in the sensed position of the throttle shafts as the throttle valves open and close which produces inaccuracies in the sensed position of the throttle valves.
The thin band also is susceptible to thermal deformation from engine heat conducted through the throttle shaft. Such thermal expansion and contraction introduces additional inaccuracies in the sensed valve position and exacerbates the hysteresis that occurs as the throttle valves open and close.
In addition, the use of a throttle sensor alone does not allow for precise control of the fuel/air mixture delivered to the cylinders of the engine. As noted above, the engine control system uses the sensed opening degree of the throttle valves to determine the time duration for which the fuel injectors should be opened in order to produce the desired fuel/air ratio. The amount of injected fuel, however, also depends upon the pressure differential between the fuel pressure within the injector and the atmospheric air pressure within the manifold. If the engine control system assumes a constant atmospheric air pressure and the fuel system does not adjust for changes in atmospheric air pressure, the engine control system cannot precisely control the fuel/air mixture when the watercraft is operated at various altitudes, such as, for example, when the watercraft is operated both in an ocean and in a mountain lake.